1. Field of the Invention
The present invention relates to a dielectric ceramic composition used in an electric device, such as a multi-layer chip capacitor, an electric device using the dielectric ceramic composition and a method of producing the electric device, particularly relates to a dielectric ceramic composition used in a multi-layer chip capacitor suitable for high frequencies.
2. Description of the Related Art
Heretofore, a variety of dielectric ceramic materials have been widely used as a material for a multi-layer chip capacitors. Since electric devices used in mobile communications, such as a cellular phones, are driven in high frequency ranges, development of dielectric materials suitable for high frequency ranges has been increasing.
As characteristics of a dielectric ceramic material used in high frequency ranges, it is desired to have an appropriate dielectric constant xcex5r, a large dielectric loss Q, a resonance frequency temperature coefficient TCf being close negatively and positively to 0 (NPO). For example, BaTi4O9+ReO based compositions and MgTiO3xe2x80x94CaTiO3 based compositions, etc. have been developed as compositions fulfilling the above requirements.
However, the burning temperature of these compositions is extremely high at 1300 to 1400xc2x0 C., so that Pd or Pdxe2x80x94Ag alloy, etc. which have a high melting point have to be used as an internal conductive metal inside a multi-layer chip capacitor.
Other than the above, development has been also made of CaZrO3xe2x80x94SrZrO3 based materials with the assumption of being used as an internal conductor of Ni as disclosed in Japanese Examined patent Publication (Kokoku) No. 7-66693, however, the materials are burned at 1300 to 1400xc2x0 C.
Also, development of CaSrxe2x80x94ZrTixe2x80x94Mn based materials is disclosed in the Japanese Unexamined Patent Publication (Kokai) No. 60-131708. In this publication, a dielectric ceramic composition for a capacitor using Ni as a terminal electrode is disclosed. The burning temperature of the Ni terminal is 800 to 1000xc2x0 C., while the ceramic composition is burned at 1350xc2x0 C.
Since the above Pd, Ni, etc. have a high conductive resistance, when used as an internal electrode of a multi-layer chip capacitor, the ratio of an electrode loss becomes larger than that of a dielectric loss in a high frequency range. As a result, the Q value of the capacitor becomes smaller, it is not possible to make the most of the excellent high frequency characteristics that the dielectric materials originally have, and it has been difficult to use it in high frequency circuits.
Thus, such metals having a low conductive resistance as Cu and Ag have been proposed. When using Cu or Ag as an internal electrode, however, the burning temperature of the dielectric material must not be more than 1000xc2x0 C. It is because when exceeding 1000xc2x0 C., the metals are exposed to the temperature ranges higher than or closer to their melting points, so that defaults are caused due to particles melting or becoming ball-shaped, and thus the metals cease to function as electrodes.
In the case of dielectric ceramic composition disclosed in the above Japanese Examined patent Publication (Kokoku) No. 7-66693, it was difficult to attain a burning temperature of 1000xc2x0 C. or less while maintaining the desired electric characteristics.
An object of the present invention is to overcome the above disadvantages by providing a dielectric ceramic composition able to be burned at a relatively low temperature of 1000xc2x0 C. or less both in air and in a non-oxidizing atmosphere, having a high Qf value and a small temperature coefficient TCf.
To attain the above object, an electric ceramic composition of the present invention, comprises a main component expressed by a composition formula [SrZrO3]x+[CaTiO3](1xe2x88x92x) wherein xe2x80x9cxxe2x80x9d indicating a mole ratio in the composition formula satisfies 1.00xe2x89xa7xxe2x89xa70.60 and a sub component including at least B2O3, SiO2 and Li2O and satisfies
1.80 greater than axe2x89xa70.25
1.80 greater than bxe2x89xa70.20
1.80 greater than cxe2x89xa70
1.10 greater than dxe2x89xa70
6.30 greater than exe2x89xa70.05
10.00 greater than a+b+c+d+exe2x89xa70.50
Where a content ratio of B2O3 is xe2x80x9caxe2x80x9d parts by weight, a content ratio of SiO2 is xe2x80x9cbxe2x80x9d parts by weight, a content ratio of ZnO is xe2x80x9ccxe2x80x9d parts by weight, a content ratio of Al2O3 is xe2x80x9cdxe2x80x9d parts by weight and a content ratio of Li2O is xe2x80x9cexe2x80x9d parts by weight with respect to 100 parts by weight of said main component.
The dielectric ceramic composition of the present invention is able to be burned at a relatively low temperature of 1000xc2x0 C. or less, has a high Qf value (for example Qf=2000 or more), a desired dielectric constant (for example xcex5r=24 to 80) and a temperature coefficient TCf which is +300 to xe2x88x9280 ppm/xc2x0 C. Accordingly, the dielectric ceramic composition can be preferably applied to a multi-layer chip capacitor having Cu, Ag, etc. as an internal conductor, and particularly applied to an electric devices used in high frequency regions.
Further, in the case of a dielectric ceramic composition wherein the value of the above xe2x80x9cxxe2x80x9d satisfies 1.00xe2x89xa7xxe2x89xa70.90, the Qf value further increases (for example Qf=4000 or more) and the temperature coefficient TCf becomes +100 to xe2x88x9280 ppm/xc2x0 C., so that the characteristics of the dielectric ceramic composition become still better.
An electric device according to the present invention comprises an internal electrode layer and a dielectric layer, wherein
said dielectric layer comprises:
a main component expressed by [SrZrO3]x+[CaTiO3](1xe2x88x92x), wherein xe2x80x9cxxe2x80x9d indicating a mole ratio in the composition formula satisfies 1.00xe2x89xa7xxe2x89xa70.60; and
a sub component including at least B2O3, SiO2 and Li2O,
and satisfies:
1.80 greater than axe2x89xa70.25
1.80 greater than bxe2x89xa70.20
1.80 greater than cxe2x89xa70
1.10 greater than dxe2x89xa70
6.30 greater than exe2x89xa70.05
10.00 greater than a+b+c+d+exe2x89xa70.50
xe2x80x83Where a content ratio of B2O3 is xe2x80x9caxe2x80x9d parts by weight, a content ratio of SiO2 is xe2x80x9cbxe2x80x9d parts by weight, a content ratio of ZnO is xe2x80x9ccxe2x80x9d parts by weight, a content ratio of Al2O3 is xe2x80x9cdxe2x80x9d parts by weight and a content ratio of Li2O is xe2x80x9cexe2x80x9d parts by weight with respect to 100 parts by weight of said main component.
Preferably, said internal electrode layer contains Cu and/or Ag.
A method of producing an electric device according to the present invention, comprises the steps of:
preparing a material of a main component expressed by a composition formula [SrZrO3]x+[CaTiO3](1xe2x88x92x) wherein xe2x80x9cxxe2x80x9d indicating a mole ratio satisfies 1.00xe2x89xa7xxe2x89xa70.60,
preparing a material of a sub component including at least B2O3, SiO2 and Li2O, and satisfying
1.80 greater than axe2x89xa70.25
1.80 greater than bxe2x89xa70.20
1.80 greater than cxe2x89xa70
1.10 greater than dxe2x89xa70
6.30 greater than e greater than 0.05
10.00 greater than a+b+c+d+exe2x89xa70.50
xe2x80x83where a content ratio of B2O3 is xe2x80x9caxe2x80x9d parts by weight, a content ratio of SiO2 is xe2x80x9cbxe2x80x9d parts by weight, a content ratio of ZnO is xe2x80x9ccxe2x80x9d parts by weight, a content ratio of Al2O3 is xe2x80x9cdxe2x80x9d parts by weight and a content ratio of Li2O is xe2x80x9cexe2x80x9d parts by weight with respect to 100 parts by weight of said main component;
obtaining a dielectric layer paste by mixing the material of the main component with the material of the sub component;
obtaining an internal electrode layer paste;
preparing a green chip to be an element body after being burned having a dielectric layer and an internal electrode layer by using said dielectric layer paste and internal electrode layer paste; and
burning said green chip at a temperature of 900 to 1000xc2x0 C.
Preferably, Cu and/or Ag is contained as an electroconductive material when preparing the internal electrode layer paste.
Note that in this specification, respective oxides composing the main component and the sub component are expressed by a stoichiometry composition, but oxidizing conditions of the respective oxides may be outside of the stoichiometry composition. Note that the above ratios of the respective sub components are obtained by measuring respective metal amounts included in the oxides composing the respective sub components and converting them to the amount of the respective oxides of the above stoichiometry composition.